1. Technical Field
The present disclosure relates to a communication system, and more particularly to a transceiver and a communication apparatus used for a communication system wherein data encoded by a transmission line code of which signal level changes at a bit boundary is transmitted/received.
2. Description of the Related Art
Conventionally, as an on-vehicle communication system, transmission line using bus-line such as CAN (control area network), LIN (Local Interconnect Network) have been employed. For example, a technical document, ‘On-vehicle Network System Detailed Explanation’ written by Michio Sato, CQ Publishing Co., Ltd, published on Dec. 1, 2005 discloses the configuration of the above-described communication system using the bus-line in detail. In the communication system, generally, a node that constitutes the communication system includes a transceiver that transmits/receives data via the transmission line and a controller that performs communication with other node via the transceiver.
In this type of communication system, to perform efficient communication, operations of transceivers disposed at the respective nodes for transmitting and receiving signals via a communication bus are desired to be synchronized with each other. As a method to synchronize the operations of the transceivers disposed at the nodes, any one of nodes transmits a signal encoded by the transmission line code including a clock component, to the transmission line, and the other node extracts the clock component from the signal on the transmission line. Then, the other node processes the free-running dock generated at the own node (e.g., divides frequency), thereby generating a bus clock that synchronizes to the extracted clock component. Hence, the transceiver can be operated based on the bus clock.
As a configuration for such a high performance transceivers, an internal clock generated by an individual clock source which is integrated therein may be employed. In this case, in order to process the signal supplied by the controller, the internal clock should be synchronized to a reference clock used for a transmission data supplied by the controller and for generating the transmission data.
However, when the encoding is performed with the internal clock that is synchronized to the reference clock, an error of the clock component included in the encoded signal is substantially the same as an error of the internal clock being superimposed to the reference clock.
As a clock source used for the controller, generally, a crystal oscillator that generates a clock signal having a precise frequency is employed. However, as a clock source used for transceivers, to reduce manufacturing cost, an oscillator circuit having less frequency-accuracy compared to that of the crystal oscillator is used.
Accordingly, at a node that operates with the clock component extracted from the signal received via the transmission line, the accuracy of the clock regenerated from the clock component degrades so that the encoded transmission data received via the transmission line cannot be sampled at an appropriate timing. Therefore, according to the above-described communication system, the following problems arise. That is, accuracy of decoding process may degrade, and higher communication speed cannot be accomplished when the accuracy of the decoding process is secured.